This is a randomized, double-blind, placebo-controlled trial of oral memantine taken alone or concurrently with an antiretroviral regimen in subjects with ADC stage 1, 2, or 3. This study will assess the possible efficacy of oral memantine in ameliorating AIDS Dementia, assess the possible efficacy of oral memantine in ameliorating painful peripheral neuropathy in HIV-infected subjects with ADC, and correlate dosing levels of memantine with observed toxicities and clinical outcomes.